A typical turbofan engine includes a core engine, a fan and a mixed flow exhaust system. The exhaust system includes an exhaust duct whose forward or upstream end circumscribes an internal mixer. A typical mixer features a set of circumferentially distributed lobes that define circumferentially alternating primary and secondary chutes. During operation, the core engine exhausts a primary stream of hot, high velocity combustion products into the primary chutes. Concurrently, the fan exhausts a secondary stream of relatively cool, relatively low velocity bypass air into the secondary chutes. The circumferentially alternating primary and secondary chutes promote thorough, circumferentially uniform mixing of the combustion products with the bypass air, which results in enhanced propulsive efficiency and reduced exhaust noise.
In some airplanes an engine mounting strut and an associated fairing span radially across the secondary air stream. The fairing intrudes axially into the portion of the mixer occupied by the lobes and also has a considerable circumferential width, typically about the same circumferential width as two or three mixer lobes. As a result of this intrusion, the engine manufacturer is unable to provide effective secondary chutes in the vicinity of the fairing. Instead, the mixer has only a single, circumferentially wide lobe and a corresponding wide primary chute in the vicinity of the fairing. The wide primary chute and the absence of secondary chutes compromise the ability of the mixer to uniformly and thoroughly mix the primary and secondary fluid streams. This results in diminished propulsive efficiency and elevated acoustic emissions.
What is needed is a fluid mixer capable of achieving thorough, circumferentially uniform mixing despite the presence of obstructions in the vicinity of the mixer lobes.